Air plenum



FIG. 1 is a perspective view of an air plenum showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a back elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design. 

CLAIM The ornamental design for an air plenum, as shown and described. 